Gradebook

Short version:
Can a calculated item in the Gradebook access the subtotals in an Advanced Grading method? i.e.  Marking Guide.  

Long version:
We are using a Forum activity, with Advanced Grading --> a Marking Guide.  The Marking Guide has three criteria, each weighted differently.  Instead of just displaying the total Forum grade in the Gradebook, I've tried to add a calculated item but would like to access the subtotals from the Marking Guide, weight them, then display a single total to students.

Then do this for the three other assessed forums.

Then display the Forum totals as another calculated item. 

Possible you think?